In prior art injection molding technology, solid molding compounds are used to fill a cavity of a mold. More particularly, a solid molding compound is compressed at a pre-heated temperature to form a compound melt before introducing the compound melt under pressure via runners into a cavity defined in a mold. After the molding compound is cured within the cavity of the mold to form an element, the cured molding compound is separated from the cavity of the mold. However, with such prior art technique, the molding compound has to be melted before the melt is introduced into the cavity of the mold through the runners. Thus, the molding process is relatively time consuming. Still further, the molding compound forms a residue in the mold, such as in the runners or molding pot, after the molding process is complete. This results in an increased expense for cleaning the mold.
U.S. Pat. No. 3,608,150 (L. Laufer et al.), issued on Sep. 28, 1971, discloses a molding process utilizing a liquid molding compound (feeding material). FIG. 1 (labeled Prior Art) herein shows a structure for the molding apparatus of the L. Laufer et al. patent. The molding apparatus of FIG. 1 comprises a storage tank 41, an injection cylinder 411 with a reciprocally movable piston 412 therein and a check valve 413, a nozzle housing 42 defining a bore 422 wherein a spring-loaded check valve 421 is positioned, and a mold 43 defining a first sprue-like runner 431 and a second runner 432 leading to a plurality of mold cavities 44. More particularly, a liquid molding compound is stored in the storage tank 41 and is introduced into the injection cylinder 411 under the control of a spring-loaded check valve 413 when the piston 412 is moved to the right in FIG. 1. Concurrently with the piston 412 moving towards the right in injection cylinder 411, the liquid molding compound in the bore 422 of the nozzle housing 42 is prevented from returning to the injection nozzle 411 by the spring-loaded check valve 421. The liquid compound is periodically introduced into a mold 43 via the nozzle housing 42 and the check valve 421 by moving the piston 412 in the injection cylinder 411 to the left after the injection cylinder 411 has been filled. A concave first runner 431 is disposed at a convex coupling portion of the nozzle housing 42 and the mold 43 to receive a charge of the liquid molding compound. A rear end of the first runner 431 is connected to a second runner 432. The liquid molding compound is charged into a plurality of cavities 44 of the mold 43 via the second runner 432. In this prior art molding apparatus, the liquid molding compound must pass through the first and second runners 431 and 432 in order to reach the plurality of cavities 44 of the mold 43. This causes the formation of a residue within the runners 431 and 432. As a result, a shortcoming of this prior art process is that the residue remaining in the runners 431 and 432 is not fully used for molding the elements, and, in turn, the molding compound is not efficiently used. Still further, since the mold compound passes through the check valve 421, around the spring therein, and eventually cures, the reliability of the spring and then the check valve is considerably affected. Additionally, since injection pressure is developed from a single cylinder 411, a pressure variation occurs in different ones of the cavities 44 as the molding compound flows through the runner 432.
U.S. Pat. No. 4,996,170 (J. Baird), issued on Feb. 26, 1991, relates to a molding process for encapsulating semiconductor devices using a thixotropic compound. FIG. 2 herein (labeled Prior Art), shows a structure for the molding apparatus of the J. Baird patent. The molding apparatus of FIG. 2 comprises a feed pot 51, a check valve 513, a transfer cylinder 52 including a reciprocative piston 521, manifolds 53, and a mold 54. The feed pot 51 stores a thixotropic compound 512 used for the molding process, and includes a follower plate 511 to prevent exposure of the compound 512 to the surrounding atmosphere. The transfer cylinder 52 includes the reciprocative piston 521 which is used to extract the thixotropic compound from the feed pot 51 via a check valve 513 in a feed tube 522. The piston 521 also functions to force the thixotropic compound to the manifolds 53 via the feed tube 522 once the manifolds 53 are in contact with the mold 54. More particularly, feed runners 531 in the manifolds are aligned with, and are sealed to, subrunners 541 in the mold 54 so that the pressurized thixotropic compound in the feed runners 531 of the manifolds are charged into the subrunners 541 and associated cavities 542 in the mold 54. After the thixotropic compound is charged into the cavities 542 of the mold 54, the thixotropic compound must be cured before the manifolds 53 and the mold 54 are separated. Thus, it takes a longer time for each compound charging step because of the waiting time for the thixotropic compound to be cured in the mold 54. Still further, in such prior art process, a multiple charging of the thixotropic compound is used, but a residue of the thixotropic compound cannot be avoided as a result of the thixotropic compound being passed through the subrunners 541 where the compound remains. Although, this prior art molding process uses multiple injection points in the manifolds 53, pressure variations can occur as the molding compound flows through the feed tube 522 and the manifolds 53.
It is desirable to provide a molding apparatus for the production of various elements, such as semiconductor elements, comprising a mold defining one or more mold cavities therein, and an injection nozzle, where the injection nozzle can be separated from the mold prior to the curing of an injected mold compound in the one or more cavities. Still further, it is desirable to provide a molding apparatus that facilitates automatic production of various elements, such as semiconductor elements, and allows high efficient use of a molding material by reducing any residue in the nozzle or runners in the mold to a minimum.